1. Field of the Invention
The present invention relates generally to an exposing device which adopts an electrophotographic method, and an image forming apparatus including the exposing device, and more particularly to an exposing device using a light-emitting element as an exposure light source, an image forming apparatus including the exposing device, and a driving control method of the image forming apparatus.
2. Description of the Related Art
Various kinds of electrophotographic image forming apparatuses (printing apparatuses), wherein organic electroluminescence (hereinafter referred to as “organic EL”) elements, for instance, are used as light-emitting elements, have been designed and manufactured as products. This type of image forming apparatus is configured such that a light-emitting element array, which is composed of a plurality of light-emitting elements, and a photoconductor drum are disposed via a lens, with a predetermined distance therebetween. Light emitted from each light-emitting element is focused via the lens, and radiated on the photoconductor, thus forming an electrostatic latent image.
Conventionally, the shape of a part, which emits light from each of the light-emitting elements of the light-emitting element array, is, in general, substantially squared. Ideally, such design is made that light emitted from the light-emitting element is focused on the peripheral surface of the photoconductor drum via the lens, thereby exposing the photoconductor and forming a substantially circular beam spot on the photoconductor drum.
A rod lens array, which is composed of a plurality of arrayed rod lenses, is used as the lens that is used in the above-described image forming apparatus. In the case of the rod lens array, it is very difficult, for the reason of manufacture, to uniformize the optical characteristics of respective rod lenses, such as refractive index distributions and tilt angles of optical axes. Consequently, the shapes of beam spots, which are actually formed on the photoconductor drum via the respective rod lens of the rod lens array, have some distortions associated with the respective rod lenses. As a result, the uniformity in print density corresponding to the respective light-emitting elements is degraded, leading to non-uniformity in print results.